1. Technical Field
The present invention relates to an electro-optical device, such as a liquid crystal device in which a driving transistor having a lightly-doped drain (LDD) structure is provided in a pixel portion, to a method of manufacturing an electro-optical device, and to an electronic apparatus including an electro-optical device.
2. Related Art
In general, in electro-optical devices, in order that an on current is suppressed from being decreased at the time of performing inversion control of liquid crystal in pixel portions and an off current is decreased, a thin-film transistor having an LDD structure is formed in each of the pixel portions. According to this LDD structure, a gate electrode is used as a mask, and regions whose impurity concentrations are different from each other are formed in a semiconductor layer.
Further, JP-A-2002-368125 discloses a semiconductor device, such as a static random access memory (SRAM), including gate electrodes having a plurality of layers having the same width.
In a liquid crystal device that is an example of an electro-optical device, light that is emitted from a light source, such as a backlight and the like, is irradiated onto a pixel region that forms an image display region. This light has high directivity and strong intensity. Accordingly, when the light is irradiated onto a semiconductor included in a transistor having an LDD, a light leakage current may be generated, and thus an image display defect, such as a flicker, may easily occur. In a lightly doped region of the semiconductor layer where impurities are doped with a relatively lower density than the other regions, a light leakage current may be easily generated, and it is difficult for the lightly doped region to be sufficiently shielded from the light by only a light-shielding unit, such as a light-shielding film or the like.
In this case, a method of shielding light by a gate electrode is also considered. However, due to the restriction of manufacturing processes when the LDD structure is manufactured and the restriction of an electrode structure of a gate electrode, it is difficult for the lightly doped region to be sufficiently shielded from the light. For example, when an electrode structure of a gate electrode disclosed in JP-A-2002-368125 is applied to the transistor having the LDD structure, since a plurality of layers forming the gate electrode have the same width, it is not possible to shield from light the lightly doped region not overlapping the gate electrode in plan view, from the design viewpoint of the LDD structure and the manufacturing processes.